Comorbidity has been identified as a poor prognostic factor for substance abusers. Although research documents that Post-Traumatic Stress Disorder (PTSD) is a common co-diagnosis, little is known about its impact on drug and alcohol use following inpatient substance abuse treatment. Using a clinical sample of substance abusers with and without a comorbid diagnosis of PTSD, the proposed project aims to assess between-group differences in treatment outcome, coping style, and relapse prevention coping skills. Study findings will be used to enhance our understanding of factors affecting relapse risk and to guide treatment interventions which will address the specific needs of substance abusing patients with concurrent PTSD. This longitudinal study includes 184 adult male and female substance abusers recruited from an inpatient treatment program. The proposed protocol compares substance abusers with and without a comorbid PTSD diagnosis on drug and alcohol use status at six-months post-treatment. It is hypothesized that, compared to non-PTSD substance abusers, substance abusing PTSD patients will evidence (1) poorer outcome at six-months follow-up; and (2) more emotion-focused, avoidant coping styles as well as less effective skills for coping with high risk relapse situations. As part of secondary analyses, the present investigation will explore the relationship between the three PTSD symptom constellations and substance abuse treatment outcome. It is hypothesized that relapse will be more likely among those whose PTSD is characterized more by avoidance symptomatology (Criterion C) than by reexperiencing (Criterion B) or hyperarousal (Criterion D) symptomatology. Other secondary analyses will examine the influence of specific PTSD-related factors (e.g., trauma magnitude, PTSD severity and chronicity, post-trauma social support) and gender on subsequent substance abuse outcome. Finally, using Marlatt's taxonomy, compare the self-reported antecedents of relapse for PTSD versus non-PTSD substance abusers who use alcohol and/or drugs during the study's follow-up period.